[Gmsh] mesh size in openCascade units

[Lukas van de Wiel]

Dear all,

I am trying to make a model existing of a quarter cylinder with a small
hole in it, at the axis.
To move along with times I have created this with openCascade blocks:

//------------------------------------------------------------------------------------------------------

SetFactory("OpenCASCADE");

chamberCenterDepth = -2000.0;
chamberMaxRadius = 1000.0;
domainLength = 15000.0;

// start with a sphere
Sphere(1) = {0, 0, -chamberCenterDepth, chamberMaxRadius};

// flatten it  {centerx, centery, centerz} {scale x, scale y, scale z}
Dilate {{0, 0, -chamberCenterDepth}, {1,1,0.5}} { Volume{1}; }

// quarter cylinder
Cylinder(2) =   {0,0,0,0,0,domainLength,domainLength,0.5*Pi};

// remove the cavity
BooleanDifference(10) = { Volume{2}; Delete; }{ Volume{1}; Delete; };

//------------------------------------------------------------------------------------------------------

So far, the geo file looks great.
However, I want a mesh that is really fine around the chamber, and that
gradually becomes coarser toward the edge of the cylinder.

I have of course read
http://gmsh.info/doc/texinfo/gmsh.html#Specifying-mesh-element-sizes
prior to using this mailing list, which resulted in failed attempts such as:

Characteristic Length {Volume{2};} = 500;
Characteristic Length {Volume{1};} = 50;

How should I go about this?

Thank you for your time and expertise!

Lukas
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